Ah, in that case, I think you were mostly on the right track except with the buffering thing and the end case for the for loop.

$| = 1;
foreach my $letter (split '', $string) {
    print $letter;
    sleep 1;
}
[download]

Somewhat obscure, but I think the following is cute:

sleep($|=print) for split '', $string;
[download]

print returns 1 if it's successful.

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'